Field
This disclosure relates generally to data processing, and more specifically, to a data processing system with built-in self-test (BIST) and method therefor.
Related Art
Logic built-in self-test (LBIST) is a type of BIST that has the testing hardware and software built into an integrated circuit (IC) being tested so that an expensive and sophisticated external tester is not needed. Like BIST, LBIST uses a scan chain of series-connected flip-flops for testing. Test data is generated in the IC and output data from the scan chain is compared with expected output data. Unexpected results from the test data input and output comparisons are used to locate problems in the IC.
For various reasons, sometimes the unexpected results from scan chain comparisons may not be an indication of a problem with the function of the IC. For example, an IC may have problems that cause the scan chain to capture an unexpected value even though normal function of the integrated circuit operates correctly. The problems may include timing problems, incorrect device modeling, or use of a poor coding style when designing the IC. These unexpected results may cause flip-flops in a scan chain to capture the unexpected value without creating an error in the function of the IC. However, the captured unexpected values may cause scan chain output comparisons to fail, leading to LBIST failure.
Fixing the problem of scan chain errors can be costly. For example, applying an engineering change order (ECO) fix may require multiple mask layers to be changed. At advanced process nodes, such as below 55 nanometers (nm), each metal layer mask may cost $125,000 or more. To avoid the cost of modifying mask layers, one or more scan chains on an IC may be disabled so that LBIST will not run for the disabled scan chain. This will significantly reduce test coverage of the IC.
Therefore, a need exists for a way to correct faulty scan chains with only a small impact to the IC design and cost, and require minimal changes to metal layers while maintaining good test coverage.